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Tuesday, January 24, 2012

Centennial of Alfred Wegener's continental drift theory: the start of Earth systems science


Alfred Wegener (1880-1930) during a scientific expedition in Greenland, in 1912. His theory of "continental drift," presented for the first time in January of that year, started a scientific revolution in geology that deeply affected the way we understand how Earth systems work. 



One century ago, in January 1912, Alfred Wegener presented for the first time his theory of "continental drift" at a meeting held in Frankfurt, in Germany (*). Wegener had collected geological and paleontological data that gave weight to an old observation: that the margin of continents on the opposite sides of the Atlantic Ocean seemed to correspond; as in a gigantic puzzle. Accordingly, Wegener proposed that the present continents were once joined together but had slowly drifted away from each other over hundreds of millions of years. (image source: J. Floor Anthony)




The story of the theory of continental drift spans several decades. Initially rejected by a majority of geologists, it gradually gained acceptance, until it became standard in the 1950s. Later on, it became part of what we call today "plate tectonics" which is a pillar of everything that we know in Earth systems science.

Occasionally, the troubled story of Alfred Wegener's theory has been perversely appropriated by climate deniers to claim that they are discriminated by the scientific establishment. But that only shows that climate deniers don't understand how science works. All new scientific theories are subjected to close scrutiny and Wegener's one was no exception. Its acceptance took time for various reasons, including the start of the First World War, shortly after it had been presented. Mainly, however, it was because at the time of Wegener there was no evidence that continents could actually move and no proof that they actually did. When satisfactory experimental evidence on these points became available, the theory was universally accepted. It is true that the debate on continental drift was harsher than usual, but it was not different than any scientific debate, as you can read in detail at this link. Wegener himself would be appalled today if he could see his name associated to junk science, as sometimes it is (see here, for instance).

The relevance of Wegener's idea of continental drift (and of its underlying mechanism: plate tectonics) is not just related to an old scientific debate. It is the basis of the modern science of Earth's systems, which includes climate science. Continental drift is a manifestation of the dynamic forces existing inside the Earth, in the region that we call "mantle". It is because of the flow of matter from the crust to the mantle and back that the system maintains a concentration of carbon dioxide in the atmosphere sufficient to maintain plant photosynthesis. Without plate tectonics, there could be no life on Earth. Indeed, Venus and Mars have no active plate tectonics and - as far as we know - no organic life.

But plate tectonics does not just maintain some carbon dioxide in the atmosphere. It also regulates its concentration and, with it, the surface temperature of Earth. Carbon dioxide is a greenhouse gas acting as the Earth's "thermostat knob." The mechanisms of plate tectonics have slowly reduced its concentration in order to maintain an average constant temperature, despite the gradual increase of solar irradiation over geological times (some 10% each billion years). This regulation is far from being perfect: during the past Aeons, the Earth saw ice ages and very hot periods but, on the average, temperatures remained within the bounds necessary for life to exist. Unfortunately, this regulation mechanism is too slow to remedy to the perturbation we are causing today to climate by our carbon dioxide emissions. Still, what we know about the mechanism of plate tectonics and its consequences on the past history of our planet should make us more careful about what we are doing now to the ecosystems. This knowledge goes back, ultimately, to the work of Alfred Wegener: scientist and pioneer of Earth systems science.

You can read how modern Wegener's view of Earth systems science was from this excerpt from UCMP (University of California Museum of Technology)


"Scientists still do not appear to understand sufficiently that all earth sciences must contribute evidence toward unveiling the state of our planet in earlier times, and that the truth of the matter can only be reached by combing all this evidence. . . It is only by combing the information furnished by all the earth sciences that we can hope to determine 'truth' here, that is to say, to find the picture that sets out all the known facts in the best arrangement and that therefore has the highest degree of probability. Further, we have to be prepared always for the possibility that each new discovery, no matter what science furnishes it, may modify the conclusions we draw."



* Wegener, Alfred (1912). "Die Herausbildung der Grossformen der Erdrinde (Kontinente und Ozeane), auf geophysikalischer Grundlage" (in German). Petermanns Geographische Mitteilungen 63: 185–195, 253–256, 305–309. Presented at the annual meeting of the German Geological Society, Frankfurt am Main (January 6, 1912).

13 comments:

  1. Nice tribute Ugo.
    In 1961 I had my first introduction to the view just taking hold, and even then we could begin to see the profound implications for understanding the ages of the world and the evolution of life. And we were just agricultural students! Our excellent Prof of Geology here in UK told us though, circa 1961, that he could still at that stage get fired if he taught it as 'knowledge', so he presented it, in some detail, as a discussion of evidence and scientific method. Lessons I never forgot.
    phil

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  2. I have some confused memories about the 1960s (I was in my teens). I distinctly remember having read about continental drift; described as real. I also remember having read a confutation of the theory, later on. That disappointed me because I liked the idea of the "puzzle" of the continents. So, it is hard to tell the story of the theory in the non-English speaking world. Perhaps it was smoother here.

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  3. Ugo,

    Another interesting article. I am becoming a regular reader of your blog.

    This sentence in the penultimate paragraph

    "Without plate tectonics, there could be no life on Earth."

    set me off on a Google search (not, I hasten to add, a proper literature search). I found some links that at least indicated that plate tectonics and life could have started around the same time.

    http://serc.carleton.edu/NAGTWorkshops/earlyearth/questions/tectonics.html
    http://my.opera.com/nielsol/blog/2008/11/27/plate-tectonics-start
    http://specialpapers.gsapubs.org/content/440/281.short
    http://www.geotimes.org/feb08/article.html?id=nn_tectonics.html
    http://en.wikipedia.org/wiki/Timeline_of_evolution

    Am I correct in thinking that any relationship between plate tectonics and life is an active area of research?

    In the process of my search, I had a look for the origin of chemical stereoselectivity (L-amino acids, D-sugars) in life. I didn't find much definitive material.

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    1. Thanks, Mike. It is a pleasure to hear that my modest work is appreciated!

      About your question, I am not a specialist in this subject, but I find it hugely interesting and I try to keep in touch with the literature - as much as I can. As far as I can say, yes, the interaction of the geosphere and the biosphere is a subject where research is being performed - the fascination lies in the wide breadth of the concept and on its interdisciplinary character. With the recent discoveries of extra-solar planets, the question of plate tectonics has taken a new interest - is there plate tectonics on these planets? Most likely, yes, although I am afraid it will not be soon when we'll have proof of that (but, on the other hand, you never know!).

      About the origins of life, it seems we are still stuck. We haven't advanced very much after the experiments by Miller and Urey in the 1960s; which in the end turned out to be based on a wrong interpretation of what the early Earth atmosphere was. My impression is that a new revolution is brewing in this area, but we are not there yet

      Anyway, if you are interested in this subject, the book by Robert Berner "the Phanerozoic carbon cycle" is a bit dated (2001) but it remains a must read.

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    2. Thank you Ugo.

      I checked on Amazon for Professor Berner's book and it costs £76. Ouch, and I live a long way from a library that would stock it.

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  4. Well, that's a problem with scientific books and scientific papers. I bought that book when I still had research funds in relative abundance. Now, I couldn't afford it myself. It is part of the great scandal of the scientific editorial system. Scientific editors, so far, have exploited scientists charging awful prices for texts that they got for free. That has to change; sooner or later. At least, one of the good things of the present crisis is that it will make these aberrant policies impossible to sustain.

    Anyway, you can get a good idea of the themes treated by Berner from the first 2-3 chapters of the (much cheaper) book by Nick Lane "Oxygen, the molecule that made the world". And the remaining chapters of that book are even more interesting!!

    (note, incidentally, that the editor of Lane's book can make a profit selling the book at less than 20$ - and they have to pay royalties to the author!)

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    1. Thank you, Ugo. I've ordered a copy of Nick Lane's book.

      Re: prices charged for scientific books. There are a number of openly available books online of which David Mackay's is one of the more well known. Others could follow that example.

      For publications, the tools have been available for about 20 years (since the graphical interface to the Web became available) for researchers to publish online. I suggest that all that has been lacking is the will!

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  5. Yes, it is the will that is lacking, but it is a complex issue. For scientists, papers are a form of currency and they don't want it debased - correctly. That doesn't mean, however, that they have to feed a band of parasites who live on that exigence.

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  6. hey ugo. I'm a teen who is doing a project, i actually found this really helpfull because you get right to the point. One thing I wasn't really happ was that you didn't put the specific date he died at or when he was actually born, but rather than that I actually enjoy your writing. Cheers.:}

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  7. Come on, Tyler! It is written in the first line; just under the picture. Alfred Wegener (1880-1930). He died rather young, but he had a very interesting life. Good luck with your project!

    Ugo

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  8. he died in 1931 not 1930

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  9. Hi, I'm currently doing some project work on Alfred Wegener for school. Is there any actual scientific experimental data which exists with which he tried to prove his theory at the time?

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  10. Anyone out there have a thesis for me on the pangea break up?

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